This invention relates to electrochemical generators or batteries. In particular, it relates to separators use in combination with electrochemical batteries such as silver/zinc batteries.
Cellulosics, such as cellophane or sausage casing, are almost exclusively used at present as main separator materials in silver/zinc batteries. However, cellulose such as cellophane is not stable in the alkaline electrolyte environment which is employed in such batteries. It degrades slowly, even in the absence of oxygen, and, of course, the presence of oxygen in the electrolyte markedly speeds up the rate of degradation of the cellulose. Additionally, because silver oxide of the positive electrode in these batteries is sufficiently soluble in the battery electrolyte, degradation of the cellulose is further increased by the presence of such a strongly oxidizing metallic oxide in the electrolyte. The silver oxide attack takes the form of deposits of metallic slver in the cellophane which lead to short-circuit failure.
In U.S. Pat. No. 3,013,099, issued Dec. 12, 1961, and entitled "Separator for Electrical Batteries", there is described an improved separator material which provides an improvement in the functioning of electrochemical batteries in general and silver/zinc batteries in particular. As described therein, a silver cellulosate separator is made by causing silver particles to react with the aldehyde groups present in the cellulose chain to produce a silver salt. This modified cellulose is more resistant to oxidation and hydrolysis than is cellophane. In spite of this improvement, the theoretical useful life of silver/zinc batteries is believed to be substantially longer than the life of presently available silver/zinc batteries. Therefore, there remains a need for an even better separator for such batteries.